Ok, I took a simple example and it worked.

I also found out that there is a message when compiling and it says that the main java class could not be copied.
Could not copy source file: C:\DOKUME~1\me\LOKALE~1\Temp\ZXing8549959346563402013temp\ZXing.java

I tried to take one of an exported applet and copied it to the lib directory of my application but it did not help.

Any ideas what is wrong with the not exportet java file?

Ok, looks like the implementation of ZXing seems to be the problem.

I use the Demo from here (server demo)

http://dev.postspectacular.com/hg/

He has a folder 'code' inside his project, there is a file called core.jar which is needed to access the ZXing library. I tried to copy it to the application folder, at some places, but did not help either. But I wonder about the folder code and if this is the right way to include the ZXing library. I tried to live without it by copying the data from the ZXing package (http://code.google.com/p/zxing/) to the library folder but I failed. Did copy the folder com form javase into there and some other ways (the zxing itself etc.) but when running my project (after restart processing) it says the library is missing.